Autofocus lens system

ABSTRACT

An autofocus lens system includes no conventional moving parts and has excellent speed and low power consumption. The system includes a small electronically-controlled focusing-module lens. The focusing-module lens includes two adjustable polymeric surfaces (e.g., two adjustable-surface lenses in a back-to-back configuration). The curvature of the surfaces can be adjusted to change focus. The performance of the autofocus lens system is extended by adding a conventional first and second lens, or lens group, on either side of the focusing-module lens. What results is an autofocus lens system with excellent near field and far field performance.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. patent applicationSer. No. 14/264,173 for an Autofocus Lens System for Indicia Readersfiled Apr. 29, 2014 (and published Oct. 29, 2015 as U.S. PatentPublication No. 2015/0310243), now U.S. Pat. No. 9,224,022. Each of theforegoing patent application, patent publication, and patent is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to indicia readers and, more particularly,to an autofocus optical system that extends the range of distances atwhich indicia may be read.

BACKGROUND

Indicia readers (e.g., barcode scanners, OCR scanners) fall into twomain classes based on their barcode-reading technology, namely (i)linear scanners (e.g., laser scanners, 1D imagers) and (ii) 2D scanners(e.g., 2D imagers, page scanners).

Laser scanners use fast moving mirrors to sweep a laser beam across alinear barcode. The bars and spaces of the barcode are recognized basedon their respective reflectivity. In other words, the light areas anddark areas of the barcode reflect light back toward the scannerdifferently. This difference can be sensed by the scanner'sphoto-detector (e.g., photodiode) and converted into an electronicsignal suitable for decoding.

Imaging scanners were developed to read advanced codes by adaptingtechnology used in digital cameras. Imaging scanners take a picture ofthe entire barcode, and a processor running image processing algorithmsrecognizes and decodes the barcode. This digital approach overcomes manyof the laser scanner's limitations.

Imaging scanners are more reliable than laser scanners, which usefast-moving parts. Imaging scanners can be configured to process allbarcodes within a field of view and do not require separate scans foreach barcode. Sophisticated decoding algorithms eliminate the need toalign the imaging scanner with the barcode. Imaging scanners can alsoscan poor quality or damaged barcodes faster and more reliably thanlaser scanners. Further, the imaging scanner is more versatile and canbe configured to address new codes or new modes of operation, such asdocument-capture. In view of these advantages, many users prefer theimaging scanner. The imaging scanner, however, lacks the extended scanrange associated with laser scanners.

Extended scan ranges are important in warehouse environments, wherebarcoded containers may be stacked on high shelves. Operators may belimited in their access to barcodes and must scan over a range ofdistances. In these situations, scanning ranges can be 10 centimeters to10 meters. This multi-order-of-magnitude range requirement placesstringent demands on the imaging scanner.

The range of imaging scanners is limited by the scanner's imaging optics(e.g., lens). The quality of a barcode image is crucial for properscans. Images that are unfocused images can render a barcode unreadable.

The range of distances over which a barcode can be decoded is known asthe working-distance range. In fixed-lens systems (i.e., no movingparts), this working-distance range is the distance between the nearestfocused objects and the farthest focused objects within the field ofview (i.e., depth of field). The depth of field is related to the lens'sf-number. A lens with a high f-number has a large depth of field. Highf-number lenses, however, collect less light. Imaging scanners mustcollect sufficient light to prevent noisy images. These scanners,therefore, need a lens with both a low f-number and the ability toproduce sharp images over a wide range of working distances. Fixedlenses, therefore, are not used for imaging scanners intended forextended range applications (e.g., warehouses).

Autofocus (i.e., AF) lenses may be used in imaging scanners that needboth near and far scanning capabilities. Typically, focus is achieved inan autofocus lens by mechanically moving the lens. Thesemechanically-tuned autofocus lenses provide range to imaging scannersbut also have some limitations.

The moving parts in mechanical autofocus lens systems may havereliability issues. The mechanical autofocus lens systems can be bulkybecause of the extra components required for motion (e.g., actuators,tracks, and linkages). These motion components also consume power at arate that may limit their compatibility with battery-powered scanners.The mechanical motion of the lens or lenses can be slow and may hindertheir use in applications that require fast focus (e.g., scanning inmoving environments). Finally, the cost of these mechanical autofocuslens systems can be high because of the number and precision of therequired mechanical parts.

Therefore, a need exists for an imaging-scanner autofocus lens systemthat has (i) a large focus range, (ii) a small size, (iii) low powerconsumption, and (iv) reduced mechanical complexity.

SUMMARY

Accordingly, in one aspect, the present invention embraces an autofocuslens system for an imaging scanner. The autofocus lens system uses afirst lens (or lens group including a plurality of lenses), a secondlens (or lens group including a plurality of lenses), and afocusing-module lens to focus a barcode onto an image sensor. The firstlens is fixedly positioned along an optical axis. The second lens isfixedly positioned along the optical axis. The focusing-module lens isfixedly positioned along the optical axis between the first and secondlenses. The lenses together create a real image of indicia. Thefocusing-module lens is used to change the focus of the autofocus lenssystem. Focus is adjusted by adjusting the optical power of thefocusing-module lens. The optical power of the focusing-module lens iscontrolled by electronically adjusting the curvature of two adjustablesurfaces.

In an exemplary embodiment, the autofocus lens system has afocusing-module lens with a clear aperture diameter that is smaller thanthe diameter of either the first lens or the second lens. Thefocusing-module lens defines the aperture stop for the autofocus lenssystem.

In another exemplary embodiment, this focusing-module lens has adiameter between 1.3 and 1.7 millimeters (e.g., about 1.5 millimeters).

In another exemplary embodiment, the autofocus lens system has a workingdistance of 10 centimeters or greater.

In another exemplary embodiment, the autofocus lens system has aresponse time of 2 milliseconds or less (e.g., less than about 1millisecond).

In another exemplary embodiment, the autofocus lens system consumes 20milliwatts of power or less.

In another exemplary embodiment, the autofocus lens system has anf-number of 7 or less.

In another exemplary embodiment, the focusing-module lens includes twoadjustable-surface lenses positioned in close proximity to one another.

In still another exemplary embodiment, the focusing-module lens mayinclude two contiguous adjustable surfaces. Here, the focusing-modulelens includes (i) a first transparent deformable membrane having aring-shaped piezoelectric film contiguously positioned on the firsttransparent deformable membrane's outer surface, (ii) a secondtransparent deformable membrane having a ring-shaped piezoelectric filmcontiguously positioned on the second transparent deformable membrane'souter surface, and (iii) a flexible polymer contiguously positionedbetween the first transparent deformable membrane and the secondtransparent deformable membrane. In this way, the flexible polymer is incontact with the inner surfaces of both the first transparent deformablemembrane and the second transparent deformable membrane. The transparentdeformable membrane can be fabricated from glass, quartz, sapphire orother semi-rigid transparent material. The two adjustable surfaces ofthe focusing-module lens may, in some embodiments, be electronicallycontrolled independently.

In another aspect, the present invention embraces an active autofocussystem for an imaging scanner including the foregoing autofocus lenssystem. In this active autofocus system, a range finder senses the rangeof a barcode through transmitted and received radiation and creates arange signal representing the sensed range. A processor generates acontrol signal based on the comparison of the range signal with a lookuptable stored in memory. The lookup table contains focus settingsassociated with various range-signal values. A controller responds tothe control signal by creating electronic autofocus signals to adjustthe autofocus lens system to achieve focus of a real image of a 1D or 2Dbarcode.

The foregoing illustrative summary, as well as other exemplaryobjectives and/or advantages of the invention, and the manner in whichthe same are accomplished, are further explained within the followingdetailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a block diagram of an active autofocussystem.

FIG. 2 graphically depicts a perspective view of a cutaway layout of anadjustable-surface lens.

FIG. 3a graphically depicts a side-view cross-section of anadjustable-surface lens with no voltage applied (i.e., the “off” state).

FIG. 3b graphically depicts a side-view cross-section of anadjustable-surface lens with a voltage applied (i.e., the “on” state).

FIG. 4 schematically depicts an embodiment of an autofocus lens system.

FIG. 5 graphically depicts a first embodiment of a focusing-module lenswith two adjustable-surface lenses in close proximity.

FIG. 6 graphically depicts a second embodiment of a focusing-modulelens.

FIG. 7 schematically depicts an exemplary embodiment of an autofocuslens system.

DETAILED DESCRIPTION

The present invention embraces an autofocus lens system for an imagingscanner that extends the range of distances over which barcodes may beread. In this regard, an exemplary autofocus lens system for an imagingscanner includes (i) a first lens (e.g., first positive lens), fixedlypositioned along an optical axis, (ii) a second lens (e.g., secondpositive lens) for creating a real image of a barcode, the second lensfixedly positioned along the optical axis, and (iii) and afocusing-module lens fixedly positioned along the optical axis betweenthe first lens and the second lens, the focusing-module lens formed fromtwo adjustable surfaces, wherein the optical power of the adjustablesurfaces is controlled electronically to achieve focus.

Imaging scanners require good images to properly decode barcodes. Theimage sensors used in these devices deliver high-quality images onlywhen the light impinging on the sensor (i) is focused and (ii) has anintensity above the sensor's noise level (i.e., a high signal-to-noiseratio).

To achieve high signal-to-noise ratio (SNR) images, the lens of animaging scanner should gather light efficiently (i.e., have a highthroughput). The entrance pupil is the image of the lens system'saperture-stop as seen through the front lens and is an indicator of thethroughput. A large entrance pupil implies that the lens system willhave high throughput. Long range scans are especially susceptible to lowSNR images. This is due to path loss. The light reflected from thebarcode spreads out over long ranges and less is captured by the scannerimaging lens. Illumination sources may help to improve the signal tonoise ratio (i.e., SNR) of images, but a high throughput imaging lens isstill extremely important.

Imaging scanners used in diverse environments (e.g., warehouses) shouldread barcodes at various ranges in both the near field and far field(e.g., 10 centimeters to 10 meters). In other words, the imagingscanner's lens must be able to create sharp barcode images over a widerange of working distances.

Fixed-focus lenses, with no focusing motion, are not used in imagingscanners requiring wide scanning ranges. These lenses typically have lowthroughput and may not be able to focus on a barcode that is close tothe scanner.

Lenses with focusing motion can extend the scanner's working-distancerange. The focusing motion moves the lens to a point where the lightrays from a barcode converge onto the image sensor and produce a sharpreal image. While this focusing movement can be accomplished manually,it is more practical for scanners to use an automatic-focus (i.e.,autofocus) system.

Autofocus systems use (i) optimal focus information and (ii) apositioner (e.g., an actuator or piezoelectric) to positioning the realimage. A passive autofocus system might use a processor runningimage-processing algorithms to determine the focus quality. Theprocessor uses this information to send signals to actuators thatposition the lens. Alternatively, an active autofocus system uses arange finder to ascertain the distance between the object and the frontlens of the system (i.e., the working distance). This range informationcan then be used to adjust the lens position for optimal focus. Becauseof its simplicity, the active autofocus scheme is well suited forimaging scanners.

The range finder in an active autofocus system can use one or moresensors to create a range signal. A processor running a process cancompare the range signal with a stored lookup table to generate acorresponding control signal. The control signal can be interpreted bycontrol electronics (e.g., a controller) to drive the lens system'spositioning devices.

A block diagram of an active autofocus system is shown in FIG. 1. Here,a range-finder 20 senses the range (i.e., working distance) of a barcodethrough some transmitted radiation 5 and received radiation 15 (e.g.,optical signals). The range finder 20 creates a range signal 25 and thensends this range signal 25 to a processor 10. The processor 10 runs analgorithm to compare the value of the range signal 25 with a lookuptable 32 stored in memory 30. The lookup table 32 contains focussettings for various range signals 25. Once the focus settingscorresponding to the measured range are determined, the processor 10sends a control signal 35 to the autofocus controller 40. Based on thissignal, the autofocus controller 40 sends electronic autofocus signals45 to the autofocus lens system 50. The autofocus signals 45 cause theautofocus lens system 50 to change the imaging system's focus. When theadjustment of the autofocus lens system 50 is complete, the light fromthe barcode 55 is well focused onto the imaging scanner's image sensor.

Autofocus functionality relies on an adjustable lens parameter to focusthe barcode. In traditional autofocus systems, focus is achieved bychanging the position of a lens (or lenses forming a lens group) inrelation to the image sensor. The autofocus signals 45 drive motors oractuators that move the lens (or lenses). In other words, the focus iscontrolled mechanically by changing the position of a lens or a lensgroup.

Mechanical autofocus systems can be bulky and slow for imaging scannerapplications. A typical mechanical autofocus system can take 60milliseconds to reach focus. Actuators in these systems can also draw arelatively large amount of power. Typical systems may draw around 450miliiwatts, which reduces battery life.

Focus can be adjustable non-mechanically as well. Lens curvature (i.e.,lens power) may be changed to adjust focus. Lenses made from anadjustable surface (i.e., adjustable-surface lenses) can be used inautofocus lens systems for imaging scanners. Adjustable-surface lensesare compact, fast, reliable, cost-effective, and energy efficient.

A perspective half-section view of a lens made from a single adjustablesurface is shown in FIG. 2. The glass support 105 is a support elementmade of a transparent rigid material such as glass. The top element is athin glass membrane 110, including an actuating element, such as aring-shaped piezoelectric film 120. The glass membrane is supported onits edges by a silicon support 115 made from some MEMS (i.e.,micro-electro-mechanical systems) manufacturing technology. Sandwichedbetween the glass support 105 and the glass membrane 110 is a flexibletransparent polymeric material 130.

The adjustable-surface lens 100 relies on a change in the polymeric,surface's curvature as a result of an applied voltage. A side-viewcross-section of the adjustable-surface lens 100 and its off/onoperation are shown in FIG. 3a and FIG. 3b respectively. As depicted inFIG. 3a , when no voltage is applied to the ring-shaped piezoelectricfilm 120, the light beam 101 passes through the clear polymer 130 withno alteration (i.e., zero optical power). On the other hand, as shown inFIG. 3b , when a voltage is applied to the piezoelectric film 120, theshape of the glass membrane 110 and the contiguous polymer 130 arecurved (e.g., spherically or near spherically). When a voltage isapplied to the adjustable-surface lens 100, the light beam 101 isfocused to a point behind the lens.

Focusing the small adjustable-surface lens 100 is achieved by changingthe shape of the adjustable surface. This change is caused by amechanical strain exerted by the ring-shaped piezoelectric film (i.e.,piezo-ring) 120 because of an applied voltage. This strain alters theshape of the glass membrane 110, and, more importantly, also changes theshape of the flexible polymer 130 that is contiguous to this layer. Inthis way, the adjustable surface's optical power is controlled, and theposition of the focus is adjusted.

The adjustable-surface lens 100 is well suited for imaging scanners. Theadjustable-surface lens 100 can be fabricated using advancedsemiconductor manufacturing techniques (i.e., MEMS technology), andtherefore can be very cost effective. The adjustable-surface lens 100 issmall and can be conveniently integrated within an imaging scanner.Adjusting the optical surface is very fast (e.g., 2 milliseconds) anddraws very little power (e.g., 20 milliwatts), allowing for fastacquisition and long-life battery operation.

The adjustable-surface lens 100 has some limitations that must beaccommodated for in order to use this component for imaging scannerapplications. The adjustable-surface lens 100 has a very small clearaperture (e.g., 1.55 millimeters) and leads to a high f-number with along focal length (e.g., f/10). The range of optical powers is limited(e.g., 0 to +10 diopters), resulting in a working distance range (e.g.,10 centimeters to infinity).

To overcome the limitation of the adjustable-surface lens's smallaperture, other lenses may be added along the optical axis 140. Anembodiment of this autofocus lens system is shown in FIG. 4. Asdepicted, the light from a barcode 55 is focused onto the image sensor155 by three ideal lenses that help to form the autofocus lens system50. A first lens 142 and a second lens 144, both with positive power,are positioned on either side of the adjustable-surface lens 100, whichhas negative power. Both the first and second lenses have apertureslarger than the aperture stop of the system (i.e., theadjustable-surface lens 100). The first lens 142 forms a large entrancepupil by magnifying the aperture stop. The larger entrance pupilimproves the lens system's throughput. The second lens 144 forms a realimage of the object (e.g., barcode) onto the image sensor 155. Afocusing-module lens 150 uses adjustable optical power to adjust thefocus position along the optical axis 140 so that, regardless of thebarcode distance, the focus position coincides with the image sensor155.

To achieve focus for all ranges, the focusing-module lens 150 must beable to adjust its optical power sufficiently. The three-lensconfiguration shown in FIG. 4 has excellent throughput but lacksperformance when a single adjustable-surface lens 100 is used. In otherwords, when a single adjustable-surface lens 100 is used, the autofocuslens system 50 cannot accommodate close scans (e.g., 10-centimeterscans). The pupil magnification, while needed for throughput, reducesthe adjustable-surface lens's ability to focus on objects in the nearfield. To extend the focus range requires optical power beyond what asingle adjustable-surface lens 100 can provide.

To increase the effective optical power, a focusing-module lens 150 maybe formed using two adjustable optical surfaces placed in closeproximity. The optical powers of the two adjustable surfaces areadditive so the overall power of the focusing-module lens 150 may bedoubled.

One exemplary embodiment of the two adjustable surface focusing-modulelens 150 uses two adjustable-surface lenses 100 placed in closeproximity (e.g., back-to-back) as shown in FIG. 5. The back-to-backadjustable-surface lenses form an effective lens with two adjustablepolymeric surfaces to control the optical power (i.e., instead of justone lens). An advantage of this embodiment is that theadjustable-surfaces lenses 100 have already been reduced to practice andare commercially available, such as from poLight AS. In this regard,this application incorporates entirely by reference U.S. Pat. No.8,045,280 (poLight AS).

Alternatively, a focusing-module lens 150 with two adjustable surfacesintegrated into a single device can be utilized. As shown in FIG. 6,this alternative embodiment includes a flexible polymer 130 sandwichedbetween two transparent deformable membranes 110, each with its ownring-shaped piezoelectric film 120. Each transparent deformable membrane110 can be fabricated from glass, quartz, and/or sapphire). Thisembodiment would allow for the same focusing power as the firstembodiment and would also offer more simplicity and compactness.

In both embodiments, the electronically controlled optical powers on theadjustable polymeric surfaces summate, thereby forming a focusing-modulelens 150 with a larger available optical power range (e.g., 0-20diopters). When this two-surface focusing-module lens 150 is used in thethree lens configuration shown in FIG. 4, the higher optical power rangeand the pupil magnification combine to form an autofocus lens system 50with excellent focus range and small f-number. Such an autofocus lenssystem is well suited for imaging scanner applications.

A practical embodiment of the autofocus lens system 50 is shown in FIG.7. Here, two positive lens groups 142, 144, including a plurality oflenses, are fixedly positioned along the optical axis 140. Afocusing-module lens 150, which includes two adjustable-surface lenses100, is fixed between the two lens groups. No moving parts along theoptical axis are required for focusing. A voltage applied to eachadjustable surface's ring-shaped piezoelectric film 120 is enough tofocus the barcode onto the image sensor 155.

The resulting autofocus lens system 50 is smaller, faster, consumes lesspower, and is more cost effective than other mechanically-tunedautofocus lenses for imaging scanners. The autofocus lens system 50,based on the architecture described here, can focus on indicia both inthe near-field (e.g., 10 centimeters) and far-field (e.g., 10 meters orgreater).

The possible applications for this auto-focus lens system 50 need not belimited to imaging scanners. Any application requiring a narrow field ofview (e.g., about 10 degrees to 15 degrees) and a wide focus range(e.g., 10 centimeters to infinity) could benefit from this lensconfiguration. For example, applications like license-plate imagers orlong range facial-recognition would be suitable for this type of lens.

This application incorporates entirely by reference the commonlyassigned U.S. Pat. No. 7,296,749 for Autofocus Barcode Scanner and theLike Employing Micro-Fluidic Lens; U.S. Pat. No. 8,328,099 forAuto-focusing Method for an Automatic Data Collection Device, such as animage Acquisition Device; U.S. Pat. No. 8,245,936 for Dynamic FocusCalibration, such as Dynamic Focus Calibration using an Open-Loop Systemin a Bar Code Scanner; and U.S. Pat. No. 8,531,790 for Linear ActuatorAssemblies and Methods of Making the Same.

To supplement the present disclosure, this application incorporatesentirely by reference the following commonly assigned patents, patentapplication publications, and patent applications:

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In the specification and/or figures, typical embodiments of theinvention have been disclosed. The present invention is not limited tosuch exemplary embodiments. The use of the term “and/or” includes anyand all combinations of one or more of the associated listed items. Thefigures are schematic representations and so are not necessarily drawnto scale. Unless otherwise noted, specific terms have been used in ageneric and descriptive sense and not for purposes of limitation.

1. A lens system, comprising: a first lens fixedly positioned along anoptical axis; a second lens fixedly positioned along the optical axis;and a focusing-module lens fixedly positioned along the optical axisbetween the first lens and the second lens, the focusing-module lensformed from two adjustable surfaces, wherein the optical power of theadjustable surfaces is controlled electronically to achieve focus, andwherein the focusing-module lens comprises (i) a first transparentdeformable membrane having a ring-shaped piezoelectric film contiguouslypositioned on the first transparent deformable membrane's outer surface,(ii) a second transparent deformable membrane having a ring-shapedpiezoelectric film contiguously positioned on the second transparentdeformable membrane's outer surface, and (iii) a flexible polymercontiguously positioned between the first transparent deformablemembrane and the second transparent deformable membrane, whereby theflexible polymer is in contact with the respective inner surfaces of thefirst transparent deformable membrane and the second transparentdeformable membrane.
 2. The lens system according to claim 1, whereinthe first lens and the second lens are positive lenses.
 3. The lenssystem according to claim 1, wherein the focusing-module lens has aclear aperture whose diameter is smaller than the diameter of either thefirst lens or the second lens, the focusing-module lens defining anaperture stop for the lens system.
 4. The lens system according to claim3, wherein the focusing-module lens has a clear aperture with a diameterof between 1.3 millimeters and 1.7 millimeters.
 5. The lens systemaccording to claim 1, wherein the first lens is a lens group comprisinga plurality of lenses.
 6. The lens system according to claim 1, whereinthe second lens is a lens group comprising a plurality of lenses.
 7. Thelens system according to claim 1, wherein the first lens and the secondlens each comprise a lens group comprising a plurality of lenses.
 8. Thelens system according to claim 1, wherein the first transparentdeformable membrane and the second transparent deformable membranetransparent each comprise glass, quartz, or sapphire.
 9. The lens systemaccording to claim 1, wherein the lens system has a working distance of10 centimeters or greater.
 10. The lens system according to claim 1,wherein the focusing-module lens has a focusing response time of 2milliseconds or less.
 11. The lens system according to claim 1, whereinthe focusing-module lens consumes 20 milliwatts or less.
 12. A lenssystem, comprising: a first positive lens group including a plurality oflenses fixedly positioned along an optical axis; a second positive lensgroup including a plurality of lenses fixedly positioned along theoptical axis; a focusing-module lens fixedly positioned along theoptical axis between the first positive lens group and the secondpositive lens group and formed from two adjustable surfaces whoseoptical power is electronically controlled to achieve focus, wherein thefocusing-module lens (i) defines an aperture stop for the lens systemand (ii) has a clear aperture whose diameter is smaller than thediameter of either the first lens group or the second lens group. 13.The lens system according to claim 12, wherein the two adjustablesurfaces of the focusing-module lens are electronically controlledindependently of one another.
 14. The lens system according to claim 12,wherein the focusing-module lens consists of two adjustable-surfacelenses positioned back-to-back.
 15. The lens system according to claim12, wherein the lens system has an f-number of 6 or less.
 16. A system,comprising: a lens system, comprising (i) a first positive lens fixedlypositioned along an optical axis, (ii) a second positive lens fixedlypositioned along the optical axis, and (iii) a focusing-module lensfixedly positioned along the optical axis between the first positivelens and the second positive lens and formed from two adjustablesurfaces, wherein the optical power of the adjustable surfaces iscontrolled electronically to achieve focus of a real image of a barcode;a range finder for sensing the range of a barcode through transmittedand received radiation and for creating a range signal representing thesensed range; a lookup table stored in memory, the lookup tablecontaining focus settings associated with range-signal values; aprocessor for running a process that compares the range signal with thelookup table in order to generate a corresponding control signal; and acontroller for reading the control signal and for outputting electronicautofocus signals to adjust the lens system.
 17. The system according toclaim 16, wherein the focusing-module lens has a clear aperture whosediameter is smaller than the diameter of either the first positive lensor the second positive lens, the focusing-module lens defining anaperture stop for the lens system.
 18. The system according to claim 16,wherein the first positive lens and the second positive lens eachcomprise a lens group comprising a plurality of lenses.
 19. The systemaccording to claim 16, wherein the focusing-module lens consists of twoadjustable-surface lenses positioned in close proximity to one another.20. The system according to claim 16, wherein the focusing-module lenscomprises (i) a first glass membrane having a ring-shaped piezoelectricfilm contiguously positioned on the first glass membrane's outersurface, (ii) a second glass membrane having a ring-shaped piezoelectricfilm contiguously positioned on the second glass membrane's outersurface, and (iii) a flexible polymer contiguously positioned betweenthe first glass membrane and the second glass membrane, whereby theflexible polymer is in contact with the respective inner surfaces of thefirst glass membrane and the second glass membrane.